1. Field of the Invention
The invention relates to a blower system and a method for controlling the same.
2. Description of the Related Art
Variable speed blowers are widely used for heating, ventilation, and air control (HVAC). The impellers of the blower rotate under the drive of a variable speed permanent magnetic motor, and the permanent magnetic motor is driven by an electric control system, that is, a motor controller. As shown in a block diagram of a current variable speed blower system of FIG. 1, the system includes an HVAC product controller, a motor controller, a permanent magnetic motor, and a blower. The HVAC product controller, which is commonly a high level product control panel, outputs an input command to control the operation of the whole product. The input command includes different operation modes of the motor, such as a constant torque mode, a constant rotational speed mode, or a constant air volume mode.
The motor controller includes a microprocessor that is used to receive the input commands and to operate the motor in a torque control mode, or a speed control mode, or in a more advanced mode, for example, air volume control mode. The motor controller further includes a frequency inverter and a sensing circuit. The frequency inverter produces a pulse width modulation (PWM) wave corresponding to different operation modes, and energizes a three-phase winding of a stator. The microprocessor detects operating current and voltage of the motor and receives feedback information through the sensing circuit, and sends out a specific control command to control the operation of the motor.
Conventional variable speed blowers employ a rotor including surface-mounted magnetic tiles. FIG. 2 shows a characteristic curve of the torque-speed of a typical variable speed blower. When the rotational speed of the motor is increased, the torque is required to increase. Thus, when the rotational speed reaches a maximum value, the corresponding torque requires a maximum torque. As shown in FIG. 2, in an operating position W1 with the maximum rotational speed S1, the rotor has the maximum torque T1. For a motor including surface mounted permanent magnets, the operating position W1 is a critical point where the frequency inverter is saturated, because the maximum rotational speed requires the maximum torque, which in turn requires a saturated voltage.
When designing a motor, the required rated torque and the rotational speed are generally considered, as shown in the curve of FIG. 2. However, optimizing the controlling strategies is seldom mentioned to extend the maximum rotational speed and torque of a motor. Furthermore, most of the motors have position sensors, thereby resulting in high material and production costs, and potential circuit failure and system efficiency reduction.
Currently, a typical motor controller employs a sensorless vector control mode, and focuses on the current vector control. However, the patent does not disclose any descriptions about using a control strategy combining the saliency of the salient pole rotor with the high flux density to improve the torque density and lower the production cost; or descriptions about the switch of a torque current control module or a direct stator flux vector control (SFVC) module according to the motor operation to improve the efficiency and lower the production cost.